documentclass[12pt,a4paper]{report}
 usepackage{mathtools, nccmath}
  usepackage{amssymb, amsthm, mathrsfs}

   begin{document}

   begin{align*}
    psicolon&mathbf{G}(p+q,d)longrightarrowmathbf{G}(q,d)times mathbf{G}(p,d)\
    &phantom{+++++}gmapstoleft(psi_1(g),psi_2(g)right),
     end{align*}
    with $psi_1(g)(j)=g(j)$ for all $1leq jleq q$ and $psi_2(g) (j)=g(j+q)$
    for all $1leq jleq p$.
      end{document}